In recent years, there has been a growing interest in high-precision infrared (IR) detectors for applications ranging from military and security to automotive and consumer markets. An infrared detector can be used for sensing of objects (for example human objects) day and night and in cases where salt, dust, heavy rain, snow, blowing sand, or petroleum vapor is present; all conditions that would seriously limit optical vision. The IR detectors are also called IR sensors and can be placed in an array to form a focal plane array. The focal plane array is the core of an IR camera and gives the camera the ability to see by forming a thermal map of the objects in the environment surrounding the device. Focal plane arrays can have various formats and pixel pitch (usually from 17 μm to 40 μm in 2010). Small format (160×120 pixels and below) arrays are typically used for building inspection, automotive, and surveillance closed circuit television (CCTV) while large format (640×480 to 1024×768) arrays are used for military and security applications. Larger or smaller pixel arrays can be used as well.
An ideal IR detector should be light, low-power, and exhibit ultra-high sensitivity. There are two main types of IR detectors: photonic detectors and thermal detectors. Thermal detectors typically do not require cooling and thus are also called un-cooled detectors. An array of thermal IR detectors is called un-cooled focal plane array (UFPA). The response time of thermal detectors is usually slow. Although the response time of thermal detectors can be improved by reducing the detector size, device scaling impairs the detection sensitivity. The response time and sensitivity of photonic detectors can be much better, but at the expense of requiring cryogenic cooling to suppress the background thermal noise. Therefore, mechanical refrigerators are usually required to maintain a stable operating temperature in photonic sensors. The refrigerator adds to the size, weight, and cost of the sensing platform. For these reasons, there is a critical need for an un-cooled IR detector that has high performance.